Electric Generators for Direct Coupled High Speed Turbo Generators in Distributed Power Systems

ABSTRACT

This article addresses various technical challenges in developing high speed, lightweight electric generators for applications in direct coupled high speed generators for distributed power systems. These challenges involve the technologies of electromagnetics, thermodynamics, rotor dynamics, and engineering assembly practices. How those challenges are being addressed and the results of activities to date relating to generators from several hundred kilowatts to a few megawatts will be discussed. Current status and the test data relating to these generators will be presented.

While the requirements of power and voltage levels as well as the duty cycle vary, the applicable generator technology is mainly impacted by the power level. The electric generator is typically driven by a high speed turbine. The operating speeds of the turbine and the mechanical and thermal interfaces with the generator have a substantial impact on the design details of the generator.

The best approach in interfacing the high speed turbine to the generator is to directly couple the two by means of a mechanical coupling and exclude the need for gear, belt or other mechanical transmission systems. The high speed turbine operates most efficiently at their rated speed, which varies with rated power output. Thus while a typical 200 kW turbine may operate at 60000 rpm, a MW class turbine may operate in the range of 15000 rpm to 30000 rpm. It is often details such as the coupling and mounting arrangement and the suitability of coolants and lubricants that affect the generator design and impact the weight and size of the final product. Selection of the appropriate generator technology is highly dependent on the operating speed requirements. Examples of specific power and speed ratings as well as suitability of generator technologies such as permanent magnet (PM), wound rotor synchronous, switched reluctance (SR) and induction will be discussed. Current development programs for 30 kW to 2.5 MW power generators will be presented.